private void btnLuu_Click(object sender, EventArgs e)
        {
            if (!Check())
            {
                return;
            }

            try
            {
                if (tinh_trang == "them")
                {
                    NHOM_HANG nh = new NHOM_HANG
                    {
                        Ma_Nhom_Hang = txtMaNhomHang.Text,
                        Ten_Nhom_Hang = txtTenNhomHang.Text,
                        Ghi_Chu = txtGhiChu.Text

                    };

                    db.NHOM_HANGs.InsertOnSubmit(nh);
                }
                else
                {
                    var nh = (from n in db.NHOM_HANGs
                              where n.Ma_Nhom_Hang == txtMaNhomHang.Text
                              select n).FirstOrDefault();

                    nh.Ma_Nhom_Hang = txtMaNhomHang.Text;
                    nh.Ten_Nhom_Hang = txtTenNhomHang.Text;
                    nh.Ghi_Chu = txtGhiChu.Text;
                }

                db.SubmitChanges();
                RaiseReloadEventHander();
                Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
        }
 partial void UpdateNHOM_HANG(NHOM_HANG instance);
 partial void DeleteNHOM_HANG(NHOM_HANG instance);
 partial void InsertNHOM_HANG(NHOM_HANG instance);